79 CHAPTER 7 The Murray Darling Depression Bioregion Murray Darling Murray Depression 1. Location 2. Climate The Murray Darling Depression Bioregion lies in the southwest corner of NSW The Murray Darling Depression Bioregion is dominated by a hot semi-arid and extends into Vic and SA. The total area of the bioregion is 19,717,651 ha climate in the northern section of the bioregion including the northeastern with 40.71% (8,026,167 ha) of this area in NSW and covering 10.03% of the arms, and a warm semi-arid climate in the southern half of the bioregion and state. eastern outliers. Small patches in the west of the bioregion fall in the NSW arid zone (Stern et al. 2000). The NSW portion of the bioregion is bounded in the north by the Broken Hill Complex Bioregion, with the Cobar Peneplain to the northeast and the Riverina Bioregion to the east. The Murray Darling Depression Bioregion also 3. Topography borders the Darling Riverine Plains to the northwest and contains outlying remnants of the Darling River and tributaries as they meet the Murray River The Murray Darling Depression Bioregion lies in the Murray Basin on Tertiary at the Victorian border. and Quaternary sediments deposited from a shallow sea, lakes and rivers.The bioregion extends into Vic and SA. The landscape is characterised by The bioregion lies entirely in the Western Division of NSW and contains few dunefields, sandplains and undulating plains of brown calcareous soils.There town centres, with Ivanhoe, just near the tip of the Riverina Bioregion, being is very little structured drainage but numerous lakes, swamps and the major settlement aside from Manilla, Emmdale and other pastoral depressions are present, some of which are driven by saline groundwater. stations in the bioregion. The bioregion includes the Murray, Murrumbidgee, Lachlan, Darling, Barwon, Yanda River and Peacock Creek catchments. Mean Annual Minimum Maximum Mean Annual Minimum Maximum Temperature Average Monthly Average Monthly Rainfall Average Monthly Average Monthly Temperature Temperature Rainfall Rainfall 16 – 19°C 2.9 – 4.9°C 32.4 – 35°C 210 – 408mm 12 – 29mm 22 – 40mm 80 The Bioregions of New South Wales – their biodiversity, conservation and history 4. Geology and geomorphology Lakes and depressions all have clay floors, and vegetation relates to the presence or absence of salt and gypsum. Infrequently flooded freshwater The Murray Basin is a shallow crustal depression filled with marine and lakes carry cane grass (Eragrostis australasica), lignum (Muehlenbeckia terrestrial sediments to a maximum depth of 600m over the last 50-60 cunninghamii) and nitre goosefoot (Chenopodium nitrariaceum), with clumps million years. Shallow seas have moved back and forth across the plains of black box (Eucalyptus largiflorens) on the margins. several times, leaving traces of parallel beach ridges and limestone sediments under the dunefields. At one stage the coast reached as far inland as The vegetation on lunettes varies. Clean sands often have white cypress pine, Balranald. while brown clayey sands support mallee with porcupine grass. Mixed sand and clay lunettes carry rosewood, belah, western pittosporum (Pittosporum Sandy surface sediments have been extensively reworked into dunes and phylliraeoides), narrow-leaf hopbush and bluebush. sandplains that have blown onto the Cobar Peneplain. Some dunes have consistent east-west linear patterns, others are parabolic, suggesting The largest rocky hills, Maccullochs Range, carry mulga (Acacia aneura) differences in vegetation cover, sand supply or age. The Darling River and dominated vegetation very similar to much of the Cobar Peneplain. Smaller streams in the Riverina have cut through the sands and constructed hills have more of a mixture of local sandplain species and distant rocky slope numerous overflow lakes such as the Sayers Lake system and the abandoned species. Pleistocene channels and basins of the Willandra Lakes complex. Saline groundwaters have formed salt basins in many places where the sandplain or 7.2 Significant flora dune topography intersects the water table. All lakes and swamps have well- Stipa nullanulla, now Austrostipa nullanulla, has been identified as regionally formed lunettes on their eastern margins that record evidence of climate endemic to the Murray Darling Depression Bioregion and is listed as change and human occupation. A few bedrock ridges rise above the endangered in the TSC Act 1995 (Bowen and Pressey 1993, cited in Morton et sandplains as isolated ranges. al. 1995). Murray Darling Murray Depression Significant flora species in the bioregion include Austrostipa metatoris, 5. Geodiversity Mossgiel daisy (Brachycome papillosa), Atriplex infrequens, and Swainsona pyrophila, all listed as vulnerable in NSW. The bioregion also supports The Murray Darling Depression Bioregion has many important wetlands. irongrass (Lomandra patens), found mainly within the Cobar Peneplain Other significant geodiversity features include: Bioregion, desert carpet-weed (Glinus orygioides), found mainly in the far flooding frequency varies and water quality and lake or swamp northwest, bluebush daisy (Cratystylis conocephala), which is very rare in environments are very diverse; NSW, Olearia calcarea, found only near White Cliffs, sand cress (Pachymitus abandoned systems, such as the Willandra Lakes, preserve evidence of past cardaminoides), Indigofera helmsii and Menindee nightshade (Solanum climates and environments along with abundant archaeology; there are karsensis) (Bowen and Pressey 1993, cited in Morton et al. 1995, Cunningham many equivalent lunette sites that have not yet been examined; et al. 1981). heavy sand mineral resources and large deposits of gypsum are known but not exploited. Other significant species are the salt pipewort (Eriocaulon australasicum) and Codonocarpus pyramidalis (Fox 1991, cited in Morton et al. 1995) as well as 6. Soils Atriplex papillata near salt lakes and the yellow Darling pea (Swainsona laxa). These are considered to be relict populations and rare in NSW, although S. Soils and vegetation differ according to the landform. On the dunefields red, laxa also occurs near Menindee in the Darling Riverine Plains Bioregion brown and yellow calcareous sands occur with more clayey materials in the (Cunningham et al. 1981). swales. On sandplains the soil tends to be heavier with brown gradational or texture contrast profiles, and mallee is found only on sandy rises. Lakes and depressions all have clay floors. The more saline lakes have grey cracking clays and carry chenopods. Salt lake floors carry little vegetation. Lunettes comprise varying soils from clean sands, brown clayey sands, mixed sand to clay. 7. Biodiversity 7.1 Plant communities Typical sandplain species include rosewood (Heterodendrum oleifolium), white cypress pine (Callitris glaucophylla), narrow-leaf hopbush (Dodonea viscosa), punty bush (Cassia eremophila), belah, copperburrs (Sclerolaena sp.), black bluebush (Maireana pyramidata) and variable spear grass. The dunes support diverse mallee (Eucalyptus sp.) communities with mixed shrubs and porcupine grass (Triodia pungens). Belah (Casuarina pauper), rosewood and variable spear grass (Stipa variabilis) occupy the swales. Photo: NPWS The Murray Darling Depression Bioregion 81 Birds of the chenopod shrublands in the bioregion seem to be at risk of decline (Reid and Fleming 1992, cited in Morton et al. 1995). Most of the extant eastern mallee (Eucalyptus sp.) and its former range (now mostly wheatfields) lies in the Murray Darling Depression Bioregion. There are several large and many small mallee remnants in the bioregion.Three bird species are found mostly or entirely in the long unburnt mallee in this bioregion; the red-lored whistler (Pachycephala rufogularis), the vulnerable mallee emu-wren (Stipiturus mallee) and the endangered black-eared miner (Manorina melanotis). Major populations of the endangered eastern subspecies of regent parrot (Polytelis anthopeplus), which moves between mallee and river red gum vegetation, are found in the bioregion. The western whipbird (Psophodes nigrogularis), the vulnerable malleefowl (Leipoa ocellata) and the endangered plains wanderer (Pedionomus torquatus), the range of which is centred on the Riverina, can also be found. More than 4% of birds observed in the bioregion are exotic species, including the Eurasian skylark (Alauda arvensis), European goldfinch (Carduelis carduelis) and the common starling (Sturnus vulgaris), all of which have adapted well to the agricultural landscapes of the bioregion. Numbers of the musk lorikeet (Glossopsitta concinna) have increased in the bioregion, as have temperate forest and temperate woodland birds. Darling Murray Depression Photo: G. Bridle Conversely, grassland, ground-nesting birds and ground-feeding insectivorous species have decreased in numbers. The general trend in this 7.3 Significant fauna bioregion is a gradual decline in numbers in isolated habitat fragments, and extinctions that occur in major mallee blocks during rare, large-scale fires.The The malleefowl (Leipoa ocellata), which is listed as endangered in the TSC Act, future of many bird populations in the bioregion may be dependent on is found throughout western NSW, including in the Murray Darling appropriate fire management as well as the restoration, expansion and Depression Bioregion (Priddel 1990, Garnett 1992, cited in Morton et al. 1995). linking of habitat fragments. The plains-wanderer (Pedionomus torquatus), listed as vulnerable in the TSC